Electrostatic incremental drive



Filed Dec. 31, 1958 0 Clutch Control Pulses r ifllllllllll-a Bios : I II I 2,995,284 ELECTROSTATIC INCREMENTAL DRIVE Ralph E. Page, LaGrangeville, N.Y., assignor to International Business MachinesCorporation, New York, N.Y., a corporation of New York Filed Dec. 31,1958, Ser. No. 784,298 15 Claims. (Cl. 226-8) This invention relates toan electrostatic incremental drive unit and has for an object theprovision of an electrostatic incremental drive suited for magnetictape.

The present invention is particularly applicable to incremental orlow-speed compatible tape drives for recording binary bits ofinformation at random time intervals. In applications of this type, themagnetic tape frequently is required to be advanced in small incrementsof about .005 inch at rates up to 500 steps per second. While precisionmechanical ratchets or escapements may perform this function, theextremely high frequency rate of operation required is not conducive tolong life. The present system does not have the above limitation and isan improvement on the apparatus described and claimed in my copendingapplication Serial No. 784,297, filed December 31, 1958. The presentform of the invention is a species disclosed and generically claimed butnot specifically claimed in copending application Serial No. 784,297,filed December 31, 1958 by Clyde I. Fitch and assigned to the sameassignee as the present application.

It is a further object of the invention to provide an electrostaticincremental drive unit suited for high fre quency rate of operation andhaving a long life.

It is another object of the invention to provide an incremental drivefor a drive member using the electrostatic principle as a brake insteadof as a driver.

In accordance with the present invention, there is provided anelectrostatic incremental drive unit suited for magnetic tape comprisinga rotor adapted for continuous rotation and having ring means thereon.The ring means includes a drive member for the tape and friction meansis disposed between the rotor and the ring means normally to drive thering means with the rotor. The ring means is adapted to carryelectrostatic resistance material in an encircling relation and aplurality of individual brake bands extend around and in engagement withthe electrostatic resistance material. The individual brake bands areadapted for selective energization alternately to lock one of the brakebands to the electrostatic resistance material for rotation with thering means. A mechanical stop means selectively engages the brake bandsto permit predetermined limited rotation of the drive member afterlocking one of the brake bands to the electrostatic resistance material.

More specifically, in accordance with one form of the present invention,the drive member for the tape is integral with the ring means and theelectrostatic resistance material is bonded thereto. The brake bands areprovided with notches or openings through which stationary stop membersare adapted to extend. The stop members are smaller than the openings topermit limited movement of the brake bands with the drive member beforebeing prevented from further rotation by engagement with the stopmembers. The brake bands have connected to one end thereof means forreturning them to their original positions after deenergization. In theform of the invention illustrated herein, the return means has beenshown as tensio n springs which are adapted to be elongated when thebrake bands are energized and locked to the drive member for rotationtherewith prior to engagement with the stop member. After a brake bandis deenergized, the tension spring is effective to return the tentPatented Aug. 8, 1961 associated brake band to its original positionwith respect to its associated stop member preparatory to a succeedingcycle of operation.

The present arrangement is particularly suited for fast operation inthat the driving and restoration of the energized and deenergized brakebands occur almost simultaneously. This is an improvement over priorarrangements where additional time was required for the slot gap in thedriving ring to fully restore to its original position before initiationof a succeeding cycle.

It is a further object of the invention to provide a control for theelectrostatic incremental drive unit whereby the energization periods ofthe brake bands overlap to delay release of one brake band whileeffecting gripping of the other brake band. Such control circuit is atype of multivibrator including a pair of gaseous discharge tubes havingtheir output circuits respectively connected to the brake bands. Inputpulses are supplied to the tubes to efliect alternate excitation of theoutput circuits and means is provided for effecting delay of release ofone brake band while effecting gripping of the other brake band. Thedelay means includes an energy storage device which dischargesalternately through the gaseous discharge tubes of the multivibrator.

For further objects and advantages and for a more detailed descriptionof the invention, reference may be had to the following descriptiontaken in conjunction with the accompanying drawing which is a schematicdiagram of the present invention showing parts thereof in perspective.

Referring to the drawing, there is shown an electrostatic incrementaltape drive unit 10 having a drive shaft 11 which is adapted forcontinuous rotation in the direction of the arrow, as by a suitablemotor and gear arrangement, not shown. The shaft 1 1 is adapted torotate at relatively slow speed, for example in the order of 60 rpm. Arotor 12 is secured to the drive shaft 11 for rotation therewith. Acylinder or ring 13 is positioned on the rotor 12 and is adaptednormally to rotate with the rotor 12 by means of friction drive sho'es15 which are carried by the rotor 12 and engage the inner surface of thering 13. The drive shoes 15 have been illustrated as curved springmembers which are secured to the rotor 12 as by screws 16.

The ring 13 is made from an electrically-conducting material such, forexample, as steel and includes as a portion thereof a drive member 13::which serves as a capstan having a rubber surfaced track area forengaging the tape T which passes therearound. The opposite end of thering 13 has bonded to the outer surface thereof a rim or sleeve 18 ofsuitable electrostatic resistance mate rial which serves as a brakeface. The electrostatic resistance material is semi-conductive, i.e.,having a resistivity within the general range of 10 to 10' ohms percubic centimeter and may be composed of a mixture of natural orsynthetic rubber, an inert filler such as asbes tos, conductiveparticles such as carbon black and a phenolic resin.

The electrostatic resistance material 18 is adapted to be engaged by apair of brake bands 19 and 20. The brake bands 19 and 20 areelectrically-conducting and preferably are made from a flexible materialsuch as thin strips of spring steel. The brake bands 19 and 20 are incontact with the electrostatic material 18 over an arc of and theelectrostatic resistance material 18 may be a single rim, as shown, orit may be divided into two separate rims each of which is engaged by therespective brake bands 19 and 20 since the material 18 acts as a pair ofbrake faces. One end of each of the brake bands 19 and 20 is connectedto a support 24 by springs 25 and 26 respectively. The opposite ends ofthe bands 19 and 20 are connected to the support 24 by springs 27 and 28respectively. The springs 25 and 26 have a relatively light tension ascompared to the heaw tension of springs 27 and 28. The ends of the bands19 and 20 adjacent the heavy springs 27 and 28 are provided withapertures or slots 19a and 20a respectively. The slot 19a is adapted tohave inserted therein a stop member 31 and the opening 20a in band 20 isadapted to receive a stop member 32. Both of the stop members 31 and 32are carried by the support 24. A brush or wiper 33 of suitable materialsuch as mohair, may be provided to Wipe the surface of the electrostaticresistance material 18 as it rotates to keep it clean.

The ring 13 is adapted to be continuously rotated by the friction drivefrom rotor 12 when not restrained by either of the two brake bands 19 or20. When voltage is applied to one of the bands 19 or 20, there isestablished a potential difference between the electrostatic resistancematerial 18 and the respective brake band creating adhesion between theband and the dielectric material 18 on the ring 13 which causes thebrake band to move with the ring and overcome the pull of the heavytension springs 27 or 28 until the stop 31 or 32 arrests this movement.This movement is predetermined by the relative size of the openings 19aand 20a in bands 19 and 20 and their respective stops 31 and 32. Morespecifically, the movement of the ring 13 is controlled by thedifference in the width of the slot 19a along the length of band 19 andthe corresponding dimension of the stop 31. Similarly, when band 20 isenergized, the movement of the ring 13 is controlled by the differencein the width of the slot 20a along the length of band 20 and thecorresponding dimension of the stop 32. As previously described, thismovement preferably is equivalent to .005 inch of capstan peripheraldistance.

In the drawing, the unit has been illustrated with a voltage applied toband 19 and the ring 13, which includes the capstan 13a, is heldstationary. A suitable switching circuit is provided for alternatelyapplying voltage to the brake bands 19 and 20. To again start movementof the capstan, a start pulse is applied to the switching circuit andvoltage is immediately applied to brake band 20. The brake band 19preferably continues to be energized for a regulated time in Order toobtain maximum adhesion between band and the electrostatic resistancematerial 18 before complete release of brake band 19. Such regulatedtime may be, for example, in the order of 150 microseconds. When thevoltage is no longer applied to band 19, the ring 13 and capstan 13awill turn and drive tape T until the band 20 has been moved into contactwith stop 32 similar to the relationship between stop 31 and band 19 asshown in the drawing. At this time the stop 32 will be in engagementwith the bottom edge of opening 20a in band 20. While the ring 13 isdriving the brake band 20 in the direction of the arrow, the brake band19 will be moved in the opposite direction by the heavy spring 27 untilmovement of the band 19 is arrested by the stop 31. At this time theupper edge of slot 19a will engage the upper surface of stop 31 and acycle of the incremental drive unit will have been completed. Thisarrangement provides for rapid response of the unit as the drive andrestoration of the bands 19 and 20 occur almost simultaneously.

Any suitable switching circuit may be employed for selectivelyenergizing the brake bands 19 and 20 in accordance with the foregoingsequence of operation. One suitable switching or control circuit hasbeen illustrated in the drawing and is of the electronic multivibratortype employing two thyratron tubes 40 and 41.

The thyratron tubes 40 and 41 of the multivibrator are each providedwith control grids 42 and 43 which are connected to the negativeterminal of a bias voltage source 44 by way of resistors 36 and 37respectively. The shield grids 46 and 47 are returned to the cathodes 48and 49 respectively of tubes 40 and 41. The cathodes 48' and 49 areconnected by way of a conductor 50 to a negative terminal of a suitablepower supply 51, the positive terminal of which is grounded. Thepositive terminal of the source of bias voltage 44 is connected to thecathodes 48 and 49 by way of conductor 52. The thyratron tubes 40 and 41are provided with output circuits which include plates 54 and 55respectively. Plate 54 of tube 40 is connected by way of conductors 56and 57 to brake band 19 and plate 55 of tube 41 is connected byconductors 58 and 59 to brake band 20. The other side of the brakecircuits is provided with a common connection to ground by way of abrush 13b which engages the conductive ring 13 on rotor 12. Thus whenthe output circuits from tubes 40 and 41 are excited, there isestablished a potential difference between the electrostatic resistancematerial 18 and the respective brake bands 19 and 20. Between plates 54and 55 of the thyratron tube 40 and 41 there is connected a capacitor orcondenser 60, the value of which is a function of the turn off time ofeach of tubes 40 and 41.

When the power of the multivibrator is first turned on, the thyratrontube 40 conducts, thus energizing the brake band 19 and locking it tothe electrostatic resistance material 18 to hold ring 13 in the positionshown in the drawing. When a positive brake control pulse is applied tothe multivibrator at 61, it passes by way of capacitor 62 to the controlgrid 43 of tube 41 and by way of conductor 63 and capacitor 64 to thecontrol grid 42 of tube 40. Since the tube 40 is already on, the controlpulse will not affect tube 40 but will turn tube 41 on. Just prior tothe turning on of tube 41, the charge on the capacitor between plates 54and 55 of tubes 40 and 41 respectively was equal to the supply voltageminus the voltage drop through tube 40. As soon as the tube 41 is turnedon, its plate voltage drops to a lower value, thus causing the capacitor60 to discharge. When this occurs, the plate voltage of tube 40 dropsbelow the value required to sustain ionization and the tube 40 turns olfleaving only tube 41 on. Thus it will be seen that the time required forthe tube which is on to turn off depends upon the deionization time ofthe tube and the value of the capacitor 60. When tube 41 is turned on,the brake band 20 becomes energized and the brake band 19 remainsenergized until the tube 40 becomes deionized. The foregoing operationis repeated when a second positive control pulse is applied to themultivibrator at 61 thereby turning tube 40 on and turning tube 41 off.Thus it will be seen that the capacitor 60 will discharge alternatelythrough the tubes 40 and 41 and this circuit will efiect delay ofrelease of one of the brake bands while effecting gripping of the otherbrake band. Stated differently, this circuit allows the on brake toremain on for a controllable time after the ott brake has been turnedon.

As may be seen in the drawing, the output circuit from tube 40 includesa diode 66 and a source of potential 67, the positive side of which isconnected to ground. It also includes a capacitor 68, one side of whichis connected to ground. Similarly, the output circuit of tube 41includes a diode 69 having a source of potential 70 one side of which isconnected to ground and a capacitor 71 also having one side connected toground. The diodes 66 and 69 and their sources of potential 67 and 70act as a clamping means for preventing excessive negative excursions ofthe thyratron plate voltage when the respective tubes 40 and 41 areturned off. The capacitors 68 and 71 likewise act as clamping means andhelp to minimize excessive negative excursions of thyratron platevoltage.

While the foregoing circuit for the electrostatic drive unit is of theelectronic type, it will of course be understood that a similar controlcan be provided by other suitable switching circuits. The delay ofrelease of one brake band while effecting gripping of the other brakeband can be obtained by employing switch contacts of the type whichmake-before-break. Thus when the contacts of the switch are beingtransferred from one position to the other, the 01f brake band will beturned on before the on brake band is turned off.

From the foregoing description it will be seen that the presentarrangement enables the driving and restoration of the brake bands tooccur almost simultaneously, thus permitting the tape to he steppedalong rapidly advancing the tape in .005 inch increments. When a blockof information is recorded on the tape it is desirable to advance thetape a substantial distance, for example about inch before recording thenext block of information. This may be accomplished by turning ofi bothof the thyratron tubes 40 and 41 and permitting the ring 13 to rotatewith the rotor 12 through the required distance be fore one of the tubesis again turned on for a succeeding cycle of operation.

It should be understood the invention is not limited to the specificarrangements shown herein and that changes and modifications may be madewithin the scope of the appended claims.

What is claimed is:

1. An electrostatic incremental drive suited for magnetic tapecomprising a rotor adapted for continuous rotation, ring means on saidrotor, said ring means including a drive member for engaging the tape,friction means between said rotor and said ring means normally to drivesaid ring means with said rotor, electrostatic resistance materialcarried by and encircling said ring means, a plurality of individualbrake bands extending around and in engagement with said electrostaticresistance material, means for alternately energizing said individualbrake bands to lock one of the latter to said ring means, mechanicalstop means supported in stationary position and spaced from said ringmeans, said mechanical stop means being effective on said brake bands intimed relation with the energization of said brake bands to permitpredetermined limited rotation of said drive member of said magneticring means and the associated one of said brake bands locked theretoafter energization of said associated brake band, and means connected tosaid brake bands to return them to their original positions afterdeenergization.

2. An electrostatic incremental drive unit suited for magnetic tapecomprising a rotor adapted for continuous rotation, ring means on saidrotor, said ring means including a drive member for the tape, frictionmeans between said rotor and said ring means normally to drive said ringmeans with said rotor, electrostatic resistance material encircling saidring means and bonded thereto, a plurality of individual brake bands inengagement with said electrostatic resistance material, said brake bandsbeing energized alternately to lock one of said brake bands to saidelectrostatic resistance material, and mechanical stop means supportedin stationary position and spaced from said ring means, said mechanicalstop means engaging said brake bands in predetermined sequence to permitpredetermined limited rotation of said drive member after locking one ofsaid brake bands to said electrostatic resistance material.

3. An electrostatic incremental drive unit according to claim 2 whereineach of said brake bands has a slot therein into which said mechanicalstop means is adapted to extend.

4. An electrostatic incremental drive unit according to claim 3 whereinsaid slots are larger than said mechanical stop means and the differencein size between said slots and said mechanical stop means determines thedegree of limited rotation of said drive member.

5. An electrostatic incremental drive unit according to claim 2including means connected to said brake bands to return them to theiroriginal positions after deenergization.

6. An electrostatic incremental drive unit according to claim 5 whereinsaid return means for said brake bands comprises tension springsconnected to one end of said brake bands to bias said brake bands in adirection opposite to the direction of rotation of said drive member.

7. An electrostatic incremental drive unit according to claim 6 whereinsaid brake bands have slots therein adjacent the ends which areconnected to said tension springs, and said mechanical stop means extendinto said slots to limit the movement of said brake bands when they areenergized and locked to said drive member and also to limit movement ofsaid brake bands in reverse direction by said springs when saidbrakebands are deenergized.

8. An electrostatic incremental drive system suited for magnetic tapecomprising a rotor adapted for continuous rotation, ring means on saidrotor, said ring means having integral therewith a drive member for thetape, frict-ion means between said rotor and said ring means normally todrive said ring means with said rotor, electrostatic resistance materialencircling said ring means and secured thereto, a pair of brake bands inengagement with said electrostatic resistance material, means forenergizing said brake bands alternately to lock one of said bands tosaid electrostatic resistance material comprising a multivibratorincluding a pair of discharge tubes, output circuits for said tubesrespectively connected to said brake bands, circuit means for supplyinginput pulses to said tubes to efiect alternate excitation of said outputcircuits, means for effecting delay of release of one of said brakebands while effecting gripping of the other of said brake bands, saidlast-named means including an energy storage device which dischargeslaternately through said discharge tubes of said multivibrato-r, andmechanical stop means effective on said brake bands to permitpredetermined limited rotation of said drive member after locking one ofsaid brake bands to said electrostatic resistance material.

9. An electrostatic incremental drive system according to claim 8wherein said discharge tubes are thyratrons, and said energy storagedevice comprises a condenser connected between the plates of saidthyratron tubes.

10. An electrostatic incremental drive system according to claim 9including diode means and a source of potential connected in circuitbetween the plate and the associated brake band to prevent excessivenegative excursions of the anode voltage of each tube as it becomesinactive.

11. An electrostatic incremental drive unit suited for magnetic tapecomprising a single cylinder of electricallyconducting material, aportion of said cylinder serving as a capstan for the tape, anotherportion of said cylinder having a sleeve of semi-conducting resistancematerial thereon, a pair of electrically-conducting brake bandsextending around said sleeve for engagement therewith, means forintermittently and alternately energizing said brake bands to establisha potential difiference between said resistance material and said brakebands for locking the energized one of said brake bands to saidresistance material, rotating means having a friction drive engaging theinterior of said cylinder to rotate said cylinder and the energized oneof said brake bands therewith, and means to limit movement or saidenergized brake band and thus limit the rotation of said cylinder andsaid tape capstan portion thereof.

12. An electrostatic incremental drive unit according to claim 11includin means connected to said brake bands for returning them to theiroriginal positions after deenergization.

13. An electrostatic incremental drive unit according to claim 12wherein said means to limit movement is characterized by said brakebands having slots therein cooperating with fixed stop members, and saidmeans for returning said brake bands to their original positionscomprise tension springs connected to said brake bands, the energizedbrake band moving against the pull of its spring and the deenergizedbrake band being restored to its original position by its spring.

14. In an electrostatic drive system suited for magnetic tape having asingle cylinder of electrically-conducting material, a portion of whichserves as a capstan for the tape and another portion of which has asleeve of semiconducting resistance material thereon, and a pair ofelectrically-conducting brake bands extending around the semi-conductingresistance material for engagement therewith, the method of advancingthe tape in predetermined increments comprising the steps of energizingone of the brake bands to lock the band to the resistance material byestablishing a potential dilference therebetween, rotating the cylinderand the brake band locked thereto through a predetermined angle ofrotation to advance the tape a predetermined increment, interrupting therotation of said cylinder, and efiecting delay of release of the lockedbrake band from the resistance material While effecting gripping of theother brake band on the resistance material.

15. In an electrostatic drive system suited for magnetic tape having asingle cylinder of electrically-conducting material, a portion of whichserves as a capstan for the tape and another portion of which has a.sleeve of semiconducting resistance material thereon, and a pair ofelectrically-conducting brake bands extending around the semi-conductingresistance material for engagement therewith, the method of advancingthe tape in predetermined increments comprising the steps of energizingone of the brake bands to lock the band to the resistance material byestablishing a potential difierence therebetween, rotating the cylinderand the brake band locked thereto through a predetermined angle ofrotation to advance the tape a predetermined increment, interrupting therotation of said cylinder, effecting delay of release of the lockedbrake band from the resistance material while efliecting gripping of theother brake band on the resistance material, rotating the cylinder andthe other brake band through a predetermined angle of rotation, andconcurrently returning the released brake band to its original positionpreparatory to repeating the foregoing cycle.

References Cited in the file of this patent UNITED STATES PATENTS1,871,272 Jongedyk Aug. 9, 1932 2,073,983 Anderson Mar. 16, 19372,338,305 Simmon Jan. 4, 1944 2,541,013 Clutz Feb. 13, 1951 2,568,824Rahbek Sept. 25, 1951 2,630,512 Rahbek Mar. 3, 1953 2,850,907 FosterSept. 9, 1958 2,850,908 Foster Sept. 9, 1958 FOREIGN PATENTS 438,860Germany Dec. 28, 1926 Patent No. 2,995,284

UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION August 8, 1961Ralph E,v Page i It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 1, 'line 23,

for Serial N0o 784,297" read Serial No. 784,299 column 6,

line 4, for "brakebands" read brake bands column 6, line 23, for"laternately" read alternately si rfd and sealed this 6th day ofFebruary 1962.-

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

